1. Field of the Invention
This invention relates to canisters for containing medicinal aerosol formulations. In another aspect this invention relates to sealing members for use in such aerosol canisters. In yet another aspect this invention relates to methods of containing aerosol formulations involving 1,1,1,2-tetrafluoroethane as a propellant.
2. Description of the Related Art
Medicinal aerosol formulations are typically contained in a metal, plastic, or glass vial equipped with a metered dose valve. The valve typically is fitted to the body of the vial by crimping a valve ferrule against the body of the vial with an intermediate seal made of an elastomeric material compressed between the body and the ferrule. The intermediate seal can be in the form of a ferrule gasket placed and compressed between the top edge of the body of the vial and the opposing surface of the ferrule gasket, or it can be in the form of an o-ring placed around the body of the vial and compressed between the body of the vial and an annular flange of the valve ferrule.
Materials used as valve seals include BUNA rubbers, butyl rubbers, neoprene, and certain thermoplastic materials, such as those disclosed for such purpose in WO 92/11190 (Marecki). Medicinal aerosol formulations are sensitive to leakage of the propellant, perhaps more so than other aerosol formulations because of the need to maintain an appropriate concentration of the medicament. However, it is known that the suitability of valve seal materials for use in connection with medicinal aerosol formulations is dependent upon the propellant and other components used in the formulation (see, e.g., WO 92/11190 and WO 92/14444). As conventional propellants will soon be phased out of production, drugs for use in metered dose medicinal aerosols must be formulated using new propellants, such as 1,1,1,2-tetrafluoroethane, 1,1,1,2,3,3,3-heptafluoropropane, hydrocarbons, and the like. It is therefore necessary to devise sealing methods, materials, and vial configurations that allow long term storage of medicinal aerosol formulations based upon such alternative propellants.